This invention relates to the fabrication of microminiature devices and, more particularly, to an apparatus and a method in which fine-line patterns for integrated circuits are precisely delineated by dry etching processes.
Considerable interest exists in employing dry processing techniques for patterning workpieces such as semiconductor wafers. The interest in dry processing stems from its generally better resolution and improved dimensional and shape control capabilities relative to standard wet etching. Thus, dry etching is being utilized increasingly for, for example, fine-line pattern delineation in the processing of semiconductor wafers to form very large-scale-integrated (VLSI) devices.
Various dry etching processes that involve radio-frequency (rf)-generated plasmas in a reaction chamber are known. These so-called plasma-assisted processes include reactive sputter (or ion) etching. In reactive sputter etching, the workpieces to be patterned are placed on the rf-driven cathode electrode in the reaction chamber. In another plasma-assisted process, typically referred to as plasma etching, the workpieces are placed on the grounded anode electrode in the reaction chamber. These and other processes suitable for making VLSI devices are described by, for example, C. M. Melliar-Smith and C. J. Mogab in "Plasma-Assisted Etching Techniques for Pattern Delineation," Thin Film Processes, edited by J. L. Vossen and W. Kern, Academic Press, New York, 1978, pages 497 to 552.
As heretofore practised, plasma-assisted etching processes designed to pattern micron and sub-micron features in VLSI devices have often been plagued with relatively poor yield characteristics. One major obstacle to achieving better results in these processes has been the seemingly unavoidable presence of contaminants in the reaction chamber of the etching apparatus. These contaminants constitute, for example, pieces of material etched away from various surfaces in the reaction chamber or chemical fragments that are generated in the chamber during etching. Such contaminants can, for example, deposit on the surface of a selectively masked layer to be etched and thereby effectively inhibit etching of the unmasked portions of the layer that underlie the deposited contaminants. As a result, the pattern etched in the contaminated layer may not be a precise reproduction of the pattern formed in the overlying mask. In many cases of practical importance, the portions of the layer that are prevented by contaminants from being etched away result in unacceptable patterns being delineated in the devices under fabrication. Or some of these unetched portions, constituting slivers or so-called "grass" regions, may break off or be transported laterally or penetrate subsequent layers during the device fabrication sequence, thereby causing faults in the devices.
For these and other reasons, considerable efforts have been directed by workers in the art aimed at trying to reduce contamination effects in the reaction chamber of a plasma-assisted etching apparatus. It was recognized that such efforts, if successful, would increase the yield and thereby decrease the cost of devices made in accordance with a fabrication sequence that includes dry patterning steps carried out in such etching apparatus.